Physical vapor deposition (PVD) is a frequently used processing technique in which a metal is deposited onto a substrate. The most common forms of PVD are evaporation, e-beam evaporation, plasma spray deposition, and sputtering. Evaporation and e-beam evaporation were used extensively in the manufacture of earlier generations of medium and large scale integrated circuits, but have since been replaced by sputtering, in which semiconductor wafers are produced by the deposition or "sputtering" of a metallic layer on the surface of a silicon wafer.
Sputtering possesses a number of advantages over other types of PVD processes, including relatively high deposition rates, the ability to deposit and maintain complex alloy compositions, the ability to deposit high temperature and refractory metals, the ability to maintain well-controlled, uniform deposition on large wafers, and the capability in multi-chamber systems to clean the contact before depositing metal.
In a sputtering process, inert gas particles are first ionized in an electrical field to produce a gas plasma within a sealed deposition chamber. The ionized particles are then directed toward a source or target where the energy of these gas particles physically dislodges, or "sputters" off, atoms of the metallic source material.
In a typical PVD process chamber, major components include a stainless steel chamber that is certified vacuum-tight with a helium leak detector, a pumping capacity that is capable of reducing the chamber pressure to about 10.sup.-6 Torr or below, pressure gauges, a sputter source or target, a power supply, and a wafer holder. The sputter source and wafer holder are normally positioned facing each other. The target may be, for example, an aluminum (Al) or titanium (Ti) disc used as the sputter source for the process. The target has different sizes, for instance, a 13-inch (330 mm) target is normally used for processing an 8-inch (200 mm) wafers. The target is bonded to a backing plate and has a life expectancy depending upon the power consumption of the process and the target material used.
In recent years, more stringent requirements of film quality and increasing wafer sizes have driven the manufacturing technology away from very large batch systems toward single-wafer processing system. Many integrated process systems that combine several process technologies in a single machine are becoming available in the marketplace. In such integrated process systems, a wafer can be transported from one single-wafer process chamber or module to another through a central transfer chamber without breaking vacuum. Consequently, much of the modern processing equipment is being designed for single-wafer use in multi-chamber clustered integrated processing systems.
In a typical multi-chamber clustered integrated processing system for PVD, thin or thick metal or barrier metal films can be deposited on silicon wafers of various sizes. For instance, four PVD process chambers can be connected to a transfer chamber which is then connected to other chambers such as a pre-clean chamber, a cool down chamber, a buffer chamber for wafer handling, and a load-lock.
PVD systems of the type described above are often used to carry out different kinds of processes, i.e., different types of metals are deposited onto different kinds of substrates. Consequently, when switching between different processes, it is typically necessary to purge and clean the deposition chamber, and change target sources so that a different metal can be deposited. This presents a number of problems in assuring that the correct target material is used in the intended deposition process. When there is a change to a different deposition step or process, it may be necessary to change the target material so that the target material being deposited is properly matched to the step or process.
The problem of installing a target assembly with the correct target materials is compounded by the fact that different target materials possess essentially the same physical characteristics, thus making it difficult, and sometimes impossible for an operator to distinguish between target materials. The similarity in appearance between target materials sometimes results in the incorrect target assembly being installed on the source mounting plate, i.e., the target material is incompatible or incorrect with the process or step to be carried out.
The present invention is intended to overcome each of the deficiencies of the prior art mentioned above.
It is therefore an important object of the present invention to provide a target mounting apparatus which eliminates or reduces a possibility of installing an incorrect or unintended target assembly in a PVD process chamber.
A further object of the present invention is to provide a target mounting apparatus which provides a reminder to the equipment operator that a target assembly possessing a specific type of target material must be installed prior to commencement of the next deposition process.
Another object of the present invention is to provide target mounting apparatus that includes physical indicia which acts as positive identification of the target material carried on a particular target assembly.
A still further object of the present invention is to provide target mounting apparatus as aforesaid possessing a simple keying arrangement in which target assemblies are physically keyed to a mounting plate, consistent with the deposition process desired to be carried out.
These, and further objects and advantages of the present invention will be made clear or will become apparent during the course of the following description of a preferred embodiment of the invention.